1. Field of the Invention
The present invention relates to a communications system consisting of a plurality of communications equipment, for instance, a communications system for carrying out the communication of data between the communications equipment through a relay. In particular, the present invention relates to a method of detecting at the destination equipment the position of source equipment in a communications system. The present invention also relates to a communications system, communications equipment, and a relay suitable for implementing this method.
A "relay" referred to in the present application is the representative of a category including all devices involved in the inter-network transmission of data signals between communications equipment and which can perform relaying of data signals, addition of redundant signals to data signals, from one network to another network, and the like thus "relay" also includes such devices as repeaters. In addition, the "position" of source equipment referred to in the present invention is not restricted to the absolute or relative position coordinates of the source equipment and may include information which indicates, for example, to which node the source equipment is connected, where the node lies (in topological sense), what kind of topological relation lies between the node and a node to which the destination equipment is connected, how many relays are used to relay a frame from the source equipment to the destination equipment, how the relays function in frame process, or what the electrical or physical length the transmission line between the source and the destination equipment is. Further, the "detecting" and "specifying" of a position are also not restricted to the obtaining of information which explicitly indicates the position, but is a concept which includes the obtaining of information which implicitly indicates the position or the network segment to which the station belongs. Moreover "communications equipment" referred to in the present application is not restricted to a single unit of communications equipment. In other words, when interpreting the present invention, "communications equipment" should be taken as also including a complete communications system which generally includes a plurality of communications equipment. The "length" of preambles or postambles referred to in the present application means the length of preambles or postambles transmitted with data signals, while the "duration" of a head preamble means the number of bits included in the head preamble.
2. Description of the Prior Art
When transmitting a data signal from one communications equipment to another communications equipment, detecting the position of the source equipment at the destination equipment is often necessary. A procedure for fulfilling this requirement was disclosed in Japanese Patent Laid-Open Publication No. Sho 62-219843, in which, while using a relay capable of decoding, processing and coding a data signal to be relayed from a path to another path in a communications equipment, the following steps are performed.
In the first step, a source equipment transmits a data signal over a communications system (over a channel, to be exact). In the second step, at least one of a number of relays included in this communications system receives and decodes this data signal. In the third step, the relay appends an identification to the decoded data signal by processing the relevant data signal. In the fourth step, the relay encodes and transmits this data signal to which the identification has already been appended over the communications system. Steps 2-4 are executed by each relay the data signal passes through and thus in general a plurality of identifications are resultantly appended thereto. In the fifth step, destination equipment receives and decodes the data signal. In the sixth step, the destination equipment extracts the identifications from the decoded data signal and deciphers them to specify the relays.
For the ordinary skilled person in the art, it is obvious from the prior art publication that the above mentioned identification may be a count incremented or decremented at each relay, enabling the destination equipment to learn how many relays the received data signal has passed through. As apparently disclosed in the prior art publication, each of the above mentioned identifications may be a code unique to each relay, enabling the destination equipment to specify which relays the received data signal has passed through based on the contents or values of the identifications and, in addition, to learn how many relays the received data signal has passed through based on the number of the identification.
Although the above mentioned identification represents the number of relays involved in or relay history of the data signal transmission and is useful for the destination equipment to learn the position of the source equipment in order to append an identification according to the above mentioned procedure in each relay, a data signal must first be decoded, to enable appending the identification, and thereafter be coded, thereby introducing extended relay processing time and complicated configuration of the relaying apparatus due to, for example, the provision of a processing means for temporarily storing and thereafter processing data within a data signal.